Spinal stenosis is narrowing of the spinal canal, lateral recess or neural foramen resulting in neural compression. The clinical symptoms of spinal stenosis include extremity pain, radiculopathy, sensory or motor deficit, gait abnormalities, neurogenic claudication, bladder or bowel dysfunction. Spinal stenosis is classified as congenital, acquired or combined. There are many causes for this condition; however, the most common cause is degenerative in nature.
For the majority of patients, conservative treatments are tried first. Non-surgical management includes rest, controlled physical activity, back brace, physical therapy, non-steroidal anti-inflammatory medications and epidural injections. Surgical decompression is performed for severe disabling pain not responding to conservative treatment, progressive neurological deficit, bladder or bowel dysfunction due to cauda equina syndrome. Decompressive surgery performed under general anesthesia is not without risks, especially in the degenerative spinal stenosis patients who are usually advanced in age with multiple medical problems.
The intervertebral foramen changes significantly on flexion and extension as well as on lateral bending and axial rotation. Flexion increases central canal and foraminal dimensions, while extension decreases them. Patients seek relief for “neurogenic claudication” or leg pain, which is aggravated by walking and relieved by sitting or flexing the spine forward. Patients with lumbar spinal stenosis assume a more flexed or rounded posture as they walk. They can walk longer periods by leaning forward supported by a cane, walker or shopping cart. Frequently, the stenotic spinal segment is limited to one or two levels and it is not necessary to flex the entire spine forward or round the whole back. If the one or two involved levels of stenosis are flexed forward, the symptoms can be relieved. If only the stenotic spinal segment (or segments) is flexed forward, then an elderly patient who walks with a kyphotic spine or rounded back can stand up straight and walk without difficulty.
The treatment method of the present invention involves placing an implant device as a spacer between the spinous processes. The implant device effectively keeps the stenotic segment in the sitting or flexed position when the patient stands up. Studies of similar approaches have shown that such treatments can be effective for patients with lumbar spinal stenosis who can sit comfortably, but have difficulty standing and walking.
Previous implant devices for interspinous distraction, such as the X-Stop from St. Francis Medical Technologies, Inc., have provided symptomatic relief and improved physical function in a high percentage of patients. (Zucherman et al, Spine. Jun. 15, 2005;30(12):1351-8.) However, the previous implant devices have the potential for causing continued degeneration of the spinous processes, particularly since the interspinous surface of the spinous process is not normally a load-bearing surface. This potential problem is especially a concern in patients with osteoporosis. In addition, the X-Stop has shown an unacceptably high failure rate for treatment of lumbar spinal stenosis caused by degenerative spondylolisthesis. (Verhoof et al, Eur Spine J. February 2008; 17(2): 188-192.)